09. The Dispatcher

The Dispatcher

The SAP dispatcher is the control program which manages the resources of the R/3 applications. It works like a typical transaction monitor which receives screens and data from the presentation services and passes them to the corresponding work processes.

The main tasks of the dispatcher are as follows:

• Balanced assignment of the transaction load to the work processes
• Buffer management in main memory
• Connection with the presentation level
• Organization of the communication processes

The logical flow of execution of a user request follows:

1. Users enter data in their presentation server; the data is received by the SAPGUI, converted to a SAP format, and sent to the dispatcher using an special optimized protocol called DIAG.

2. Initially, the dispatcher keeps the requests in queues, where the dispatcher later processes them one by one.

3. The dispatcher allocates the user requests using the free work processes. The real execution takes place inside the work processes themselves.

4. At the end of execution, the result of the work process task goes back to the SAPGUI through the dispatcher. SAPGUI interprets the received data and fills up the user screen.

SAP has optimized the data flow between the presentation and the application servers. Typically the quantity of data that goes in the network from the dispatcher to the SAPGUI does not exceed 2K (for dialog processes). This network traffic does not include the print requests that are managed by spool or print managers on users' PCs or workstations.